An art operable to compress data such as images and voices is lately of significant importance to enrich our daily lives.
The current handheld terminal allows for a video-phone call between remote locations. The use of a pair of videophones allows moving images to be transmitted therebetween in synchronism with voices, whereby richly expressive communication is achievable when compared with the past handheld terminals. Each of the videophones is provided with a radio transmission channel. The radio transmission channel has the current transmission speed of 64 kbps (bit per second). In future, a transmission speed as fast as some 2 Mbps is probably achievable. To provide improved quality of each image transmitted at relatively lower speed, a moving image-transmitting art is important, and a moving image-compressing/encoding art is of particular importance.
A variety of proposals have been made to provide the moving image-encoding art. The standard specification of the image-compressing art includes H.261 and H.263 according to ITU-T (the ITU Telecommunication Standardization Sector), and MPEG-1, MPEG-2, and MPEG-4 (MPEG is short for the Moving Picture Experts Group) according to ISO (the International Organization for Standardization). H.264 (or MPEG-4 Advanced Profile) is a standardized next-generation encoding art provided by ITU-T jointly with ISO.
In general, to provide an increased compression ratio, a calculation quantity during the image encoding is required. For example, when a moving image is compressed in accordance with the MPEG-4 Advanced Profile (hereinafter called a MPEG-4 AVC), a compression ratio is improved twice as high as that according to MPEG-4 Simple Profile (hereinafter called a MPEG-4 SP), provided that image quality according to the MPEG-4 AVC is substantially similar to that according to the MPEG-4 SP. At the same time, the calculation quantity according to the MPEG-4 AVC is more than twice as large as that according to the MPEG-4 SP. More specifically, under a fixed transmission rate, the MPEG-4 AVC is better in image quality than the MPEG-4 SP, but is greater in portable terminal processing amount than the MPEG-4 SP. As a result, the MPEG-4 AVC is greater in power consumption than the MPEG-4 SP. The MPEG-4 AVC includes a large number of encoding tools, and both of the image quality and the portable terminal power consumption are considerably varied, depending upon selected one of the encoding tools during the image encoding. For example, a loop filter providing a greater processing amount but better image quality is selectively executable during the image encoding.
In portable terminal-based communication, a reduction in power consumption is of significant importance. In particular, a battery consumes a significant amount of electrical power to transmit and receive moving images because there is a need for a data quantity greater than a voice quantity as well as a need for a considerable amount of processing to compress and decompress the moving images.
Assuming that a communication counterpart is an under-qualified terminal, there are cases where such a terminal fails to decode received data when the data transmitted from the self-terminal to the communication counterpart has been encoded in accordance with an encoding method that involves a large amount of processing.
Referring to FIG. 12, an art disclosed by cited Reference No. 1 (published Japanese Patent Application Laid-Open No. 2000-341222) is illustrated. According to the disclosed art, the remaining battery power of the communication counterpart is monitored to change the encoding method in accordance with a status of the communication counterpart. The following discusses the disclosed art of cited Reference No. 1 with reference to FIGS. 12 and 13.
In FIG. 12, a portable terminal includes a remaining battery power-detecting unit 1409, a control unit 1408, and a radio communication unit 1405. The remaining battery power-detecting unit 1409 detects the remaining battery power of the portable terminal. The detected remaining battery power is fed into the control unit 1408. The control unit 1408 compares the remaining battery power with a threshold. As illustrated in FIG. 13, the radio communication unit 1405 addresses an encoding method-changing request to a communication counterpart of the portable terminal when the remaining battery power is equal to or less than the predetermined threshold.
The host apparatus includes a radio communication unit 1403, a control unit 1404, an encoding unit 1402, and an input unit 1401. When the radio communication unit 1403 receives the encoding method-changing request, then the control unit 1404 sends out control information to the encoding unit 1402. The control information requests the encoding unit 1402 to change the encoding method in mode to another mode in which the portable terminal consumes reduced electrical power to decode the data.
The encoding unit 1402 encodes the input data entering through the input unit 1401 in accordance with the instructions from the control unit 1404, thereby providing encoded data. The encoded data is sent out to the portable terminal through the radio communication unit 1403.
FIG. 13 illustrates a flow of data. As illustrated in FIG. 13, the host apparatus 1501 in the course of transmitting the encoded data at a high-bit rate is driven to switch over the encoded data from the current high-bit rate to a lower bit rate in response to a signal indicative of the encoding method-changing request from the portable terminal 1502.
Another art is disclosed in cited Reference No. 2 (published Japanese Patent Application Laid-Open No. 1994-140332). According the disclosed art, a communication rate is calculated based on the remaining battery power to compare the calculated communication rate with a communication rate of the communication counterpart, thereby selecting a smaller communication rate.
A further art is disclosed in cited Reference No. 3 (published Japanese Patent Application Laid-Open No. 1999-232071). According to the disclosed art, fewer receivable and transmittable objects are provided in accordance with the remaining battery power.
However, each of the above arts according to cited References 1-3 merely takes account of a countermeasure that portable terminals at opposite ends of communication are controlled to be mutually rendered durable as long term as possible in response to a reduction in remaining battery power in each of the portable terminals. More specifically, the intention of a user of each of the portable terminals cannot be reflected in communication control.
For example, assume that each of the users of the portable terminals thinks that communication in a standard or low quality image mode is satisfactory without the need for a high-quality image mode. However, the user can select neither a reduced power consumption-involving encoding method nor a reduced power consumption-involving decoding method.
In particular, even when the current remaining battery power is sufficient, it is impossible to postpone, as long term as possible, a stage at which the remaining battery power becomes insufficient. As a result, communication capability operable for a longer period of time is unavailable.
In view of the above, an object of the present invention is to provide a portable terminal operable to rationally determine an encoding method and/or a decoding method, and operable to communicate for a further longer period of time.